1. Technical Field
This invention relates generally to rotating dynamoelectric machines and more specifically to an improved rotor construction which exhibits reduced windage losses.
2. Background Art
Inductor type dynamoelectric machines have been employed, in the past, to realize high-speed operation, particularly for electrical generation. Such machines are generally characterized by a stator which includes both ac armature and dc excitation coils, surrounding a coil-less rotor. Since there are no rotating field or armature coils in this type of dynamoelectric machine, slip rings, brushes and associated connections, common to machines having rotating windings, may be entirely eliminated. This feature, coupled with the typical solid construction of the machine rotor, makes the inductor machine particularly adaptable to high rotational speed applications.
One known version of an inductor type dynamoelectric machine, employs a circumferentially distributed arrangement of "C" or "U" shaped armature elements surrounding a generally cylindrical field coil which in turn encloses a transverse pole magnetic rotor. U.S. Pat. Nos. 437,501, and 2,519,097 and 3,912,958 describe earlier machines of this general design. Such machines typically employed frame mounted hardware for directly supporting the individual components of the stator and suffered from deficiencies attendant to this construction.
A more recent version of such an inductor type machine is disclosed in commonly owned, U.S. Pat. No. 4,786,834, issued Nov. 22, 1988 in the name of James J. Grant, et al. The improvement described therein encompasses a spool-like support structure for supporting the field winding and armature element's from inside and for accurately positioning the armature elements. The spool-like structure is made of non-magnetic material and has a hollow, elongated central portion extending concentrically about a longitudinal axis. This central portion supports a field coil and defines an interior longitudinal passageway for accommodating the insertion of a coaxial rotor. At each end of the central portion, end portions extend radially outward therefrom. Each of these end portions is preferably provided with radially oriented grooves in its axially outermost surface. The grooves are configured to receive and orient legs of generally U-shaped armature core elements arrayed in a circumferentially distributed pattern about the periphery of the spool-like structure. The end portions of the spool-like structure are axially spaced and radially dimensioned, and the grooves in the outer face of each end portion are angularly spaced so as to precisely position the armature elements in three orthogonal directions.
For cooling purposes, cooling ports are provided in the central portion of the spool-like structure. These ports are located near the ends of the central portion and communicate with extended recesses in the surface of a unitary, transverse pole, salient, homopolar rotor mounted for rotation within the central portion. The rotor acts as an impeller and centrifugally propels cooling fluid through said cooling ports and into the vicinity of the field winding and armature coils.
Other features, aspects, advantages and benefits of this recently developed, highly acclaimed dynamoelectric machine are detailed in U.S. Pat. No. 4,786,834, the disclosure of which is incorporated by reference herein.
At high speeds, dynamoelectric machines employing salient pole rotors can experience substantial windage losses. These losses are due to air being drawn into the lowest part of the interpole recesses and then being slung outward toward the tip of the pole face. In a machine of the design of U.S. Pat. No. 4,786,834, this air is then forced to escape between the inner faces of the U-shaped armature pieces, which are only thousandths of inches from the pole tips, thus creating high windage losses, in addition to high acoustical noise. If the axial air flow to the bottom of the interpole recesses is blocked off, the majority of the windage losses due to this air path are eliminated, thus leaving more horsepower in the dynamoelectric machine for actual work.
In the past, it has been proposed to close the interpole recesses by fastening disc-like shrouds on the outside thereof or by filling the recesses with a non-magnetic material. (See U.S. Pat. Nos. 3,157,806 and 3,737,696, and NASA Report 701-011-0006-22 entitled "Prediction of Windage Power Loss in Alternators", dated July 26, 1968.) These approaches have served to reduce windage losses, but they suffer from certain shortcomings and have not been optimized to allow both for sustained high speed operation and convenient, economical construction of a rotor especially useful in a dynamoelectric machine of the type described in U.S. Pat. No. 4,786,834.